Rotatable point-attack bit with protective body

ABSTRACT

A rotatable point-attack bit retained for rotation in a block bore, and used for impacting, fragmenting and removing material from a mine wall. An improved elongated tool body having at the front end a diamond-coated tungsten carbide wear tip that is rotationally symmetric about its longitudinal axis and contiguous with a protective tungsten carbide intermediary body, which is contiguous with the third section steel shank at the rear end.

FIELD OF INVENTION

[0001] The present invention relates to a rotatable cutting bit design for use in construction and excavation of the type having an improved head portion and depending shank.

BACKGROUND OF THE INVENTION

[0002] The invention is directed to a rotatable cutting tool having a diamond coated hard carbide insert brazed to an elongated body consisting of a protective cemented carbide secondary body segment and a third steel segment. The design of the invention is to provide improved performance and safety characteristics. These characteristics include a longer performance cycle through increased wear and fracture resistance resulting in a more efficient continuously penetrating material removal cycle and an improvement in safety, due to the protective mid section, of less chance for methane gas ignition and explosion. The protective hard carbide mid section that supports the diamond coated tip not only results in increased wear life of the bit body but also serves to protect the lower steel shank in tougher milling conditions. Past applications have suffered from bit failure when the steel holding the carbide or diamond coated insert is eroded away during application, exposing the cutting insert and allowing fracture thereof thus leading to catastrophic failure of the bit. This invention of a protective carbide body holding the cutting tip and protecting the steel shank prevents erosion of support around the tip insert and erosion of steel below the carbide body thus significantly extending the life of the cutting tool. The present invention also reduced the potential of sparking and explosion from ignition of methane gas. The ignition of methane gas, which is released from pockets where the gas has been trapped in the material being mined is a safety problem. A common belief is that the primary cause of such ignition is the heat generated through friction as the bits move through the coal and rock during the mining operation. It is also possible that the sparking, which may occur when the steel base portions of the bits strike rock, causes ignition of the methane gas. Since the coefficient of friction of tungsten carbide is substantially lower than that of steel, less heat is generated as the protective body of the present invention cuts through coal and rock, thus reducing the possibility of gas ignition.

[0003] Examples of rotatable cutting tools are on applications with long wall miners, continuous miners, and road planers. A longwall mining machine is used for mining coal seems underground. The machine includes two rotating drums having a plurality of blocks affixed thereto.

[0004] Long wall mining tools typically comprise an elongated steel body with a hard cemented carbide tip brazed into a socket contained in the forward end of the steel body. One such point attack bit is described in U.S. Pat. No. 4,065,185. Attempts to improve performance have been made by hardening the insert tips of mining attack tools by the use of diamond compacts. One such diamond compact for use in cutting, machining, drilling and like operations is disclosed in Hall et al U.S. Pat. No. 4,604,106. Mining bits incorporating the diamond tips brazed onto steel inserts and subsequently brazed into steel bodies are shown in Anderson et al U.S Pat. Nos. 5,837,071 and 6,051,079.

[0005] The steel body includes a reduced diameter portion adjacent to the rearward end thereof. A retainer is adjacent the reduced diameter portion of the steel body. The retainer functions to rotatably retain the rotatable cutting tool within the bore of the mounting block during the milling operation. Each block contains a central bore therein. This and other resilient retainer means useful with the present invention are described in U.S. Pat. Nos. 3,519,309 and 4,201,421.

[0006] During the milling operation, the drums rotate so as to cause the rotatable cutting tools to impact the mine wall surface. The tools impact and fracture the wall surface. The surface fragments of coal chunks and powder are collected by a continuously moving conveyor belt and carried to the surface of the mine for processing. During the rotation of a drum, each rotatable cutting tool rotates about its central longitudinal axis. It is important that the tools continue to rotate because without adequate rotation a conventional tool will be locked into position and start an uneven wear pattern that leads to rapid tool degradation and ultimate tool failure. Due to the higher wear resistance of the protective secondary cemented carbide body segment of the present invention, the uneven wear pattern shown by conventional tools, is greatly diminished or not noticeable when the tool clears and resumes its rotation.

SUMMARY OF THE INVENTION

[0007] The present invention overcomes the shortcomings associated with known constructions and teaches the construction and operation of an insert for mining attack tools. The present invention of a protective cemented carbide mid body segment, which fully retains the diamond coated insert, and at its base is brazed to the steel shank, serves to protect the diamond coated insert from premature support erosion, and the steel shank from premature wear and failure, which is the most common mode of failure with all diamond tipped previous inventions. Thus, the protective carbide segment prevents the common failure of wash out around the tip and channels the flow of material away from the steel shank so as to significantly reduce erosive wear of the steel shank below the protective segment.

[0008] Since the coefficient of friction of tungsten carbide is substantially lower than that of steel, less heat is generated as the protective body of the present invention cuts through coal and rock thus increasing the safety of operation by reducing the potential of sparking and explosion from ignition.

[0009] The protective body is preferably formed as a unitary member of cemented carbide or other material, which provides suitable hardness and abrasion resistance characteristics, and which at the top provides a suitable base for inserting and brazing a diamond insert and at the bottom a radiused contour to allow inserting and brazing into a steel shank. The term “cemented carbide” refers to the type of material resulting when grains of carbide of the group IVB, VB, or VIB metals are pressed and sintered in the presence of a binder such as cobalt, nickel, or iron as well as alloys thereof.

DETAILED DESCRIPTION

[0010] Referring to the drawings more particularly by reference numbers wherein like numerals refer to like parts, number 3 in FIG. 2 identifies a protective hard body constructed according to the teachings of the present invention. Shown in FIG. 1 is a segmented preferred embodiment of the invention of a rotatable cutter bit 1 having a diamond coated cemented tungsten carbide tip 2 having a rearward radiused cylindrical stem surface that mates, and is brazed, into the radiused segment cavity 4 of protective middle body 3.

[0011] The cemented carbide body 3 is joined to a steel body 15 by a braze joint 6. The head portion 2, the mid section 3, and the shank 15 are coaxially aligned. The shank 15 having at its widest diameter, an enlarged section 7, which prevents the tool from being forced into the opening in the mounting block.

[0012] The rearward steel member 15 may be seen to include a generally cylindrical shank portion 16 having an annular groove 17 near the rearward end and a frusto conical portion 18 adjacent forward to the shank portion 16. The frusto conical portion 18 has a radiused socket 19 at the forward end.

[0013]FIG. 2 shows the present invention protective second or middle segment body 3, which includes a head end portion 10 which is circular, containing a cavity or radiused socket 11 to retain after brazing, the diamond coated insert which protrudes forwardly in the direction of engagement with a work surface to be mined and a tail end section 12 which is brazed into a cavity or radiused socket 19 of the steel shank 15. The head end portion of 3 has an angle A leading away from the insert cavity towards the base of the body. The resulting frusto conical surface 14 is centered about the longitudinal axis and intersects with a second frusto conical surface 20 formed by an angle B with the base that further leads down the length of the body to point 13 meeting a wider band that serves to strengthen and seat the body into the steel shank 15. The values of angle A and, or angle B will vary depending on the particular mining application. For example, a range from 30 to 60 degrees has been found by the inventor to be the most effective range for the angle A, while a range from 5-15 degrees has been found to be most effective for angle B. 

What I claim as my invention is:
 1. A rotatable cutting bit for impacting, fragmenting and removing a substrate comprising of: a ferrous body or shank having a longitudinal axis and forward end; a protective cemented carbide mid section body rotationally symmetric about said longitudinal axis; a diamond coated cemented carbide insert rotationally symmetric about said longitudinal axis.
 2. The rotatable cutting tool of claim 1 wherein the forward end of the protective body contains a seat or radiused socket defining a volume.
 3. The rotatable cutting tool of claim 1 wherein the axially rearward section of the insert has a protruding segment that generally corresponds to, and fits into, the shape of the seat or radiused socket of the protective body.
 4. A braze joint joining the protruding or radiused extension axially rearward section of the insert of claim 1 to the mating seat or radiused socket of the axially forward section of the protective body.
 5. The rotatable cutting tool of claim 1 wherein the steel third section of the tool body contains at its forward point a seat or radiused socket defining a volume.
 6. The rotatable cutting tool of claim 1 wherein the protruding shape at the base of the protective body corresponds to the shape of the seat or radiused socket defined in claim
 5. 7. The rotatable cutting tool of claim 1 wherein said protective body is affixed to the pocket of the steel shank of claim 5 by brazing.
 8. A rotatable cutting bit for impacting, fragmenting and removing a substrate comprising of: a ferrous body or shank having a longitudinal axis and forward end; a protective cemented carbide mid section body rotationally symmetric about said longitudinal axis; a diamond coated cemented carbide insert rotationally symmetric about said longitudinal axis.
 9. The protective cemented carbide mid section body of claim 8 having a forwardly facing socket extending forwardly therefrom by way of a continuous radius to the forward most point of said body;
 10. The first forwardly facing surface of the protective mid section and the mating rearwardly facing surface of the insert of claim 8 are bonded by a brazed joint.
 11. The protective cemented carbide mid section body of claim 8 having a frusto conical surface or surfaces leading from the front of the body, where it is attached to the insert, to the rear of the body, where it is attached to the steel shank. The resulting diameter at the rear of the body being larger than the diameter at the front of the body.
 12. The protective cemented carbide mid section body of claim 8 having a second rearwardly facing surface with a first rearwardly radiused surface leading to the rearwardly facing surface.
 13. The protective cemented carbide mid section body of claim 8 wherein a second rearwardly facing surface is located radially inside and rearward of the first radiused rear surface.
 14. The protective cemented carbide mid section body of claim 8 wherein the first forwardly facing surface of the steel body and the secondly rearwardly facing surface of the protective cemented carbide mid section are bonded by a brazed joint.
 15. The steel shank of claim 8 having a means for holding a loosely resilient retainer on the steel body that allows the cutter bit to rotate about its longitudinal axis in a mounting block. 